Nitrile-butadiene rubber (NBR) is an oil-resistant elastomer used in automotive applications, but has poor high temperature properties. The recommended continuous use temperature is between 100.degree.-125.degree. C. Commercially available hydrogenated NBR (HNBR) addresses the need for a higher use temperature, oil-resistant elastomer having a continuous use temperature up to about 150.degree. C.
Removal of the backbone unsaturation in NBR by hydrogenation increases the heat resistance of the polymer while maintaining its low temperature and oil-resistant properties. HNBR is mainly a random copolymer of ethylene and acrylonitrile. HNBR compositions that contain up to 40 weight percent bound acrylonitrile and 60 weight percent hydrocarbon segments have high oil resistance and good low temperature properties. Higher acrylonitrile content in the copolymer would further increase oil resistance, but would be detrimental to low temperature properties.
Thus, although NBR can be successfully hydrogenated to form HNBR having desirable thermooxidative stability or high heat-resistance, as well as high oil-resistant properties, NBR must be hydrogenated utilizing a homogeneous rhodium catalyst which is very expensive, thus making the hydrogenated copolymer product economically limiting. The economical and efficient process of the present invention cannot be utilized to hydrogenate NBR since the pendant nitrile groups of the copolymer would hydrogenate, thus lowering oil-resistance and also causing cross-linking of the polymer chains making the copolymer product unsuitable for elastomer applications. Therefore, butadiene-alkenylpyridine copolymers, butadiene-acrylate copolymers, and copolymers of butadienes with 1,3-dienes containing fluorine are hydrogenated using the process of the present invention to produce a high-temperature and oil-resistant elastomer, wherein the unsaturated olefinic backbone of each of the copolymers as well as the pendant unsaturation derived from the hydrocarbon diene, is hydrogenated to a high degree which results in the improved heat-resistance of the copolymer, without hydrogenation of the polar groups thereof thereby maintaining the oil-resistance of the copolymer. Again, these hydrogenated copolymers of the present invention are produced in an economical manner, making them more desirable than the expensive HNBR copolymers.
U.S. Pat. No. 3,416,899 (Schiff, Dec. 17, 1968) relates to improved gel compositions useful as incendiary fuels, as solid fuels for heating, as a fracturing liquid for subterranean formations, and the like. In another aspect, this reference relates to the preparation of hydrocarbon gel compositions by hydrogenating a hydrocarbon solution of an unsaturated rubbery polymer in the presence of a catalyst comprising a reducing metal compound and a salt of a Group VIII metal.
U.S. Pat. No. 3,673,281 (Bronstert et al., Jun. 27, 1972) relates to a process for the hydrogenation of polymers containing double bonds in solution and in the presence of a catalyst complex comprising:
A. a compound of iron, cobalt or nickel,
B. an organo-aluminum compound, and
C. hexaalkylphosphhoric acid triamide as activator.
Polymers of diene hydrocarbons contain double bonds in the backbone. These double bonds may be hydrogenated by conventional processes. Products which are wholly or partly hydrogenated in this way are superior to non-hydrogenated polymers in that they possess improved resistance to aging and are particularly resistant to oxidative degradation. In the case of block copolymers of dienes and vinyl aromatic compounds, in particular, the hydrogenated products also show improved tensile properties and mechanical strength. When only partially hydrogenated, the diene polymers may be vulcanized. Such vulcanizates possess a higher tensile strength and a lower glass temperature than vulcanizates of non-hydrogenated diene polymers.
U.S. Pat. No. 3,625,927 (Yoshimoto et al, Dec. 7, 1971) relates to a catalyst for hydrogenating a high molecular weight polymer having hydrogenatable unsaturated bonds. This catalyst is suitable for hydrogenation of the polymer is a viscous solution form and comprises a reaction product of (1) a metal chelate compound of nickel, cobalt, or iron, with (2) an organic metallic reducing agent in said chelate compound. The chelating agent is attached to the metal by a pair of nitrogen atoms and an oxygen atom.
U.S. Pat. No. 3,531,450 (Yoshimoto et al, Sep. 29, 1970) relates to a new hydrogenation catalyst consisting of three catalytic components and a process for hydrogenating polymers by the use of said catalyst. This three-component catalyst consists of (1) at least one kind of an unsaturated hydrocarbon selected from the group consisting of an olefinically unsaturated hydrocarbon and an acetylenically unsaturated hydrocarbon, (2) at least one kind of an organic compound of the metal selected from the group consisting of nickel, cobalt and iron, and (3) at least one kind of a metal compound reducing agent.
U.S. Pat. No. 3,766,300 (De La Mare, Oct. 16, 1973) discloses a process for the hydrogenation of copolymers prepared from conjugated dienes and certain copolymerizable polar monomers such as vinyl pyridines, acrylonitriles, and alpha-olefin oxides which comprises an initial step of forming a complex between at least one Lewis acid and the polar portions of the copolymer and thereafter subjecting the complex to hydrogenation. More particularly, this reference is especially concerned with a process for the hydrogenation of block copolymers derived from these monomers.
Japanese Patent 13,615 (Aug. 2, 1967; filed Feb. 15, 1963) relates to copolymers of butadiene and vinyl pyridine that were reduced to give waterproof, stable reduced copolymers. These products were useful for coating pills. The reduced copolymers were obtained by the catalytic hydrogenation in the presence of Raney nickel catalyst.
A paper titled "Oil-Resistant Rubbers from 2-Methyl Vinyl Pyridine," James E. Pritchard and Milton H. Opheim, Industrial and Engineering Chemistry, Volume 46, No. 10, pages 2242-2245, relates to quaternization of liquid polymers. Copolymers of butadiene and 2-methyl-5-vinyl pyridine (MVP) react with quaternizing agents to form polymeric salts of the type: ##STR1## where R is an aliphatic or aromatic radical and X represents halide, alkyl sulfate, or aryl sulfonate groups.
In addition, commercially available fluoroelastomers are synthesized by the copolymerization of fluoro olefins, for example ##STR2## Due to the saturated backbone and presence of carbon fluorine bonds, the fluoro polymers have high thermooxidative stability when compared to their hydrocarbon counterparts. The major drawback of these fluoro elastomers is their poor low temperature properties which is reflected in relatively high glass transition temperatures (Tg). The Tg's of oil-resistant non-fluorinated elastomers are lower. Nitrile (i.e., butadiene/acrylonitrile copolymer with 40 weight percent acrylonitrile) and hydrogenated nitrile rubber exhibit Tg's of about minus 30.degree. C. versus a Tg of minus 20.degree. C. for the fluorinated copolymer described above.
Elastomers derived from the copolymerization of fluorinated olefins with hydrocarbon olefins are also heat resistant due to the saturated backbone in these polymers. However, the lower the fluorine content, the lower the heat and oil resistance. Also, the glass transition temperature of these elastomers is not significantly improved when compared with the corresponding highly fluorinated counterparts.
When a hydrocarbon diene such as 1,3-butadiene bears a fluorinated substituent such as 2-trifluoromethyl, elastomeric homopolymers are obtained. Free radical polymerization can occur in a 1,2; 3,4; or 1,4 manner. Polymerization in the latter mode would lead to backbone unsaturation in the polymer, which is detrimental to the thermooxidative stability of the polymer, more so than the pendant unsaturation generated by polymerization in a 1,2- or 1,4- manner. Elastomeric polymers are also obtained when the hydrogen atoms of 1,3-butadiene are substituted with fluorine atoms (e.g., polyfluoroprene). However, these polymers also suffer from poor thermooxidative instability due to the presence of backbone unsaturation. Thermooxidative stability is increased in polymers derived from highly fluorinated 1,3-dienes, but these materials tend to be plastics.
Highly fluorinated 1,3-dienes can be copolymerized in emulsion with 1,3-diene hydrocarbons. Relatively low Tg materials can thus be obtained. For example, a copolymer of 1,1,2-trifluorobutadiene with butadiene in a 1 to 1 mole ratio has a Tg of minus 48.degree. C.
U.S. Pat. No. 3,308,175 (Barr, Mar. 7, 1967) relates to novel fluorine-substituted dienes, to a method for the preparation thereof, to certain novel intermediates and the preparation thereof, and to certain novel intermediates for the production of homologous fluorine-substituted dienes.
U.S. Pat. No. 3,379,773 (Barr, Apr. 23, 1968) relates to polymeric compositions and to processes for the preparation of those compositions. Copolymers of 1,1,2-trifluorobutadiene-1,3 and the method of preparing the same are described within this reference along with comonomers hexafluorobutadiene-1,3; 3,4-dichloro-3,4,4-trifluorobutene-1; 2,2,2-trifluoroethyl vinyl ether; vinyl chloride; styrene; 1,1,2-trifluorobutene-1; and 1,1,4,4-tetrafluorobutadiene-1,3.
U.S. Pat. No. 3,398,128 (Bolstad et al, Aug. 20, 1968) relates to halogen-containing copolymers of 1,1,2-trifluorobutadiene-1,3 and another fluorinated 1,3-diene having from 4 to 5 carbon atoms per molecule containing two fluorine atoms on a terminal carbon atom and at least one hydrogen atom and the process for copolymerization of those monomers to produce such copolymers.
U.S. Pat. No. 3,562,341 (Tarrant et al, Feb. 9, 1971) relates to incompletely polyfluorinated 1,3-dienes capable of forming crosslinked polymers and having fluorine substituents in at least the 1,1,2-position, and to synthesis for their preparation. More particularly, this reference relates to a synthesis for 1,1,2-trifluorobutadiene-1,3 and to the compounds 1,1,2,4,4-pentafluorobutadiene-1,3, and 1,1,2,4,4-pentafluoro-3-methylbutadiene-1,3.
U.S. Pat. No. 3,607,850 (Smith, Sep. 21, 1971) relates to a method of polymerizing conjugated fluorinated dienes which are rubber-like, flexible at low temperatures, and resistant to mineral oils and other chemicals. More particularly, the reference relates to use of rhodium salts or complexes as catalysts for the polymerization or copolymerization of conjugated fluorinated dienes to produce high molecular weight elastomers.